I am not sure what you expect from this kind of printer. I can see the technical appeal, but for precise printing it is maybe the worst setup i have ever seen. Long lever arms with high mass at the end and plastic connectors to the other parts. Two circular axis with the inherent numerical imprecissions.
For what it's worth, i think the result is actually pretty ok for such a setup.

... read about difference in accuracy between "normal" and "parallel" Scara robots - you have a "normal" type with typical behaviour, a parallel Scara will behave different with much more stiffness and accuracy over the working area ...

@vdx
I don't like pararel scara.
It's hard to make exactly the same length of arms, in the end hard to calibrate as delta.
I make calibration route very easy for this model and it quite accurate and only takes not more than an hour.

@VDX
I don't really understand what you mean with parallel scara reduce distance error. I think by nature parallel scara is a bit more stiff than single. but reducing distance error, I don't think it is.
I think in parallel, if I don't make the parallel arms really parallel, it would be an additional problem in calculating the error.

... no, it's more than that - a serial scara has only one "base" and suffer from any mechanical elasticity flexing the arm ... the more "stretched" it is, the more flexing through weight and dynamic forces ...

A parallel scara is not "geometrically parallel" - it has two arm bases with a distance of maybe 15% - 20% arm length and both arms are jointed in the tool center point.
This gives an enormous benefit in stiffness with stretched arms!

But you have to calculate the tool position with Inverse Kinematics, similar to a delta, to get this working with our normal XYZ positioning ...

Maybe check here [www.youtube.com] to see what kind of mechanical effort you have to make to get a single arm Scara stable.
It will never be as fast as a delta or cartesic printer.
Single Arm Scara and Parallel have very different kinematics, i am not sure which is mroe computing intensive though.
In my opinion the single arm Scara printer combine the worst aspects of all printers, closely followed by the parallel.
Do not expect it to be precise, do not epxect it to be fast. If you encrease the build area the imprecision will get worse, similar to a delta, but quicker.

When I was involved with the accuracy testing, Harmonic Drive assembled a small demonstrator to show the precision of their "harmonic gears" with a pretty nice and small setup with maybe 200mm overall footprint, 150mm square working area and sub-micron positioning accuracy

Both those examples show machines with a Z height of a very few centimeters.
If you were to use a heatbed that moves in z direction i think it can work. The OPs idea of mounting the Z axis at the end of the arm will not be able to produce quality or fast prints.